U.S. Pat. No. 5,305,047 (the '047 patent) discloses a compact light projection system for autofocus detection apparatus in which a stripe pattern is projected onto an object in a wide range. The light projection device includes a chart having a pattern to be detected, an illuminating device for illuminating the chart, and a lens assembly for projecting the pattern. The lens assembly includes a first lens having an optic axis and second and third lenses having optic axes respectively inclining at a predetermined angle to the optic axis of the first lens.
A problem with the light projection system of the '047 patent is that it uses a light emitting diode 3 (LED) as the illuminating device. Radiation emitted from an LED does not remain collimated as it emanates away from the LED. As a result, the LED radiation rapidly diffuses and therefore becomes progressively less effective in an active autofocus system as the distance increases between the image capture apparatus and the scene whose image is to be captured. A further problem is that LED 3 appears to emit infrared radiation (col. 1, 32-34) which is not visible to the unaided human eye. As such, a camera operator will not be able to tell which part of the scene the camera is focusing on.
A further problem with the '047 patent is that there will be knife-edge diffraction and scattering from the sectioning of the emitter lens which will reduce the contrast of the reflected pattern. Also, the subsectioned emitter lens does not produce beams having the same cross-section and/or intensity.